Article comprising oxide-bondable solder

ABSTRACT

The invention provides an article comprising a solder that bonds well to oxides and other surfaces to which solder bonding is problematic. The solder composition contains one or more rare earth elements, which react with the oxide or other surface to promote bonding, and further contains sufficient Au and/or Ag to act as carriers for the rare earths. Because rare earths have some solid solubility in Au and Ag, the problem of intermetallic formation is lessened or eliminated, and improved bonding to oxide surfaces is attained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to solder compositions, particularly solder compositions useful for bonding to oxides.

2. Discussion of the Related Art

Electronic solders such as Pb—Sn, Sn—Ag, Bi—Sn, and Au—Sn are widely used for bonding of components and circuits in electronic and optoelectronic devices. Numerous other solder compositions, as well as a variety of processing and assembly procedures, are also known. See, e.g., H. H. Manko, Solders and Soldering, McGraw-Hill Inc., (1992).

It is known that the nonmetallic surfaces of oxide materials prohibit direct wetting of solder, and therefore require an intermediate bonding layer, also known as a metallization layer, to allow soldering to occur. Typically, a thin metallic film layer is deposited onto the oxide surface, and any solder bonding is carried out on that metallic film. For example, soldering on silica optical fiber is able to be accomplished by forming a nickel-containing intermediate layer, e.g., by electroless plating, on the silica surface. (See, e.g., R. W. Filas, “Metallization of Silica Optical Fibers”, MRS Symposium Proc., Vol. 531, 263 (1998)). Soldering on ceramic substrates, such as Al₂O₃, in hybrid circuits is conventionally accomplished by first metallizing the oxide surface using either a thick-film technique relying on firing of a metal-glass mixture frit at elevated temperatures or a thin film technique relying on sputtering or evaporation of a metal layer. The use of such an intermediary metallization layer, however, is not always desirable due to the added complexity and cost, as well as concerns over bond reliability since there is often no strong chemical bond at the oxide-metal interface.

One approach to these metal-oxide bonding problems has been to incorporate reactive elements, such as rare-earths, into the solder. The rare-earths improve the bond by inducing chemical reactions at the interface between the metal and the oxide. (See, e.g., U.S. Pat. No. 3,949,118) Unfortunately, the matrix materials of these solders—Sn and Pb—lack solid solubility for the rare earths. And this lack of solubility makes the solders susceptible to significant loss of bonding ability, due to the tendency of the rare earths and the matrix solder to form intermetallics, which renders the rare earths unavailable to aid in the bonding process. This intermetallic formation occurs both during the manufacture of the solders—when the melt is cooled to room temperature, and also later—due to time-dependent reactions of the reactive elements during storage.

Thus, improved solder materials capable of providing reliable bonds to oxides, yet which avoid problems of previous solders, are desired.

SUMMARY OF THE INVENTION

The invention relates to use of solders containing rare earth metals. While the use of rare earths has previously been contemplated in solder, as mentioned above, problems related to rare earth's near-zero solubility in conventional solder metals have not been solved. The invention overcomes these problems by providing a solder material containing sufficient Au and/or Ag to act as a carrier for the rare earths. Because rare earths have some solid solubility in Au and Ag, the problem of intermetallic formation is lessened or eliminated, and improved bonding to oxide surfaces is attained. In particular, the solders of the invention contain typical solder metals, e.g. Sn, Pb, Sb, In, Bi, about 0.02 to 20 wt. % rare earth metals, and sufficient gold and/or silver to provide solubility for the rare earths. The resultant solder provides excellent bonding to oxide materials such as glass optical fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a Sn—Lu binary alloy phase diagram;

FIG. 2 is a Lu—Au binary alloy phase diagram;

FIG. 3 is a Lu—Ag binary alloy phase diagram;

FIG. 4A is a cross-sectional TEM micrograph showing the interfacial details of Sn—Ag—Lu solder directly bonded onto optical fiber glass (quartz).

FIG. 4B consists of TEM chemical analysis taken across the interfacial bonding region shown in FIG. 4A, establishing the participation of the rare-earth element in the bonding process.

FIGS. 5A and 5B schematically illustrate fiber grating devices comprising the oxide-bondable solder according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, solder compositions are provided with rare earth metals to make the solder reactive with an oxide surface. Suitable rare earths include Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The rare earth metals have strong thermodynamic affinity to oxygen, and thus, when present in molten solder in contact with an oxide, the rare earths take oxygen atoms away from the oxide surface, reducing the surface to a metal or oxygen-deficient oxide that is better able to bond to the solder. Improved bonding between the solder and the oxide surface is attained. Improved bonding to other problematic surfaces is also possible.

As discussed above, rare earths have essentially no solubility in the typical metals found in solder (Sn, Pb, Bi, Sb, and In), e.g., typically less than 0.01 wt. %, and also exhibit high melting points, e.g., 780 to 1660° C. (See, e.g., the Lu—Sn phase diagram of FIG. 1.) Upon being incorporated in such a solder metal, the rare earths therefore tend to be consumed by formation of intermetallics with the other solder metals. Because these intermetallics tend to be stable and have high melting points, the rare earths essentially become trapped and cannot contribute to bonding.

According to the invention, however, use of Au and/or Ag in a solder composition provides sufficient solid solubility for added rare earths to avoid such problems. (See, e.g., FIGS. 2 and 3, which are the phase diagrams for Lu—Au and Lu—Ag, respectively.) The solubility in the Au and Ag make the rare earth atoms available to diffuse out of the Au or Ag and participate in bonding reactions at a solder-oxide interface. Specifically, the solder compositions of the invention comprise one or more rare earths and sufficient Au and/or Ag to provide solubility for at least a portion (advantageously substantially all) of the added rare earths. Particularly desirable elements are those having relatively large solubility in Ag and Au: Y, Sm, Gd, Tb, Dy, Ho, Er, Tm and Yb. La, Ce, Pr, Nd, Eu tend to be less desirable due to much smaller solubility in Ag or Au. As reflected in Example 3 below, use of the solder of the invention results in an interfacial region at the solder-surface interface. The rare earth element or elements appear to segregate at the interface during soldering, thereby aiding the bonding process.

The typical amount of the one or more rare earth elements is 0.01-20 wt %, more typically 0.1-5 wt %, and even more typically 0.2-2 wt %, based on the weight of the entire solder composition, with the actual amount varying depending on, for example, the solubility of the particular rare earth element or elements in the Au or Ag, and the amount of Au or Ag present.

It is possible to base the solders of the invention on any conventional solders, e.g., elemental metals of Sn, Sb, In, Bi, Zn, Pb, Ag, or Au, or binary, ternary or quaternary solders based on Au—Sn, Pb—Sn, Bi—Sn, Sn—Ag, Sn—Zn, or Sn—Sb (eutectic or near-eutectic compositions as long as a sufficient amount of Au or Ag is present.) For example, solders in which Au or Ag are a primary matrix or primary alloying material (e.g., at least 50 wt. % Au and/or Ag) are possible, such as Au-20 wt. %Sn eutectic (m.p.=280° C.), Au-12.5 wt. % Ge eutectic, (m.p.=361° C.), Au-3.2 wt %Si eutectic (m.p.=363° C.), Au-25.5 wt %Sb eutectic(m.p.=360° C.), Au-42 wt %In (m.p.=495° C.) or Sn-3.5 wt. % Ag eutectic (m.p.=221° C.). The rare earth elements are then added as discussed above.

For solders not based on Au or Ag, e.g., Pb—Sn, Bi—Sn, Sn—Sb, or Sn—In, Au and/or Ag are intentionally added. For example, it is possible to alloy Sn-37%Pb, Pb-5%Sn, Bi-48%Sn, Sn-5%Sb, Sn-45%In, or elemental metals such as Sn or In, with Au or Ag, together with one or more of the rare earth elements. A useful range for Au and/or Ag additions in these solders is 0.1-30 wt. % Au and/or Ag, typically 0.2-5 wt %, based on the weight of the entire composition, along with the amounts of rare earth elements listed above. Thus, the solders should have at least 0.1 wt. % Au and/or Ag. For these solders, the amount of rare earths added depend on the amount of added Au or Ag, since the Au or Ag act as hosts for the rare earths. Adding too much rare earths, e.g., the top end of the above range, while adding only a small amount of Au or Ag will tend to cause the intermetallic formation discussed above. To provide useful results for solders not based on Au or Ag, the rare earths are typically added in an amount of 0.01 to 50 wt. %, based on the weight of the added Au or Ag.

Because the rare earth atoms are required primarily for interfacial chemical bonding reactions, a relatively small amount is generally sufficient. Excess rare earth atoms not dissolved in solid solution in the prepared solder alloy will typically be present as intermetallic compounds that generally do not participate in the interface bonding, but a limited concentration of such intermetallics is acceptable, e.g., less than 20 wt. %, especially if the rare-earth containing intermetallic compounds have relatively low m.p., e.g. below ˜600° C.

The solders of the invention are useful for a variety of electronic or optical device applications where there is a need to make electrical, mechanical, or thermal connections between oxide and metal or between oxide and oxide. Surfaces onto which the inventive solders are able to directly bond, without the need for an intermediate metallization layer, include SiO₂, Al₂O₃, NiO, Cr₂O₃, Fe₂O₃, Ta₂O₅, ZrO₂, CuO₂, ZnO, and compound oxides such as LiNbO₃. In addition, it is also possible to attain useful bonding to difficult-to-solder metals such as Al, Si, Ti, Cr and their alloys, which tend to easily form native oxides of Al₂O₃, SiO₂, TiO₂, Cr₂O₃ respectively, on the surface.

The solder material is prepared by conventional alloying techniques. The resultant solder is used in the same manner as conventional solders, e.g., bonding is facilitated by any conventional techniques, including a soldering iron, laser heating, infrared heating, and ultrasonic bonding. Soldering flux is typically not required, but is useful in reducing the oxidation of the molten solder, especially in air. The use of ultrasonics or other mechanical disturbances are often useful, e.g., to break up a surface oxide of a molten solder, in order to facilitate the solder-oxide interface bonding reaction. In addition, particularly in the case of optical fiber bonding, it is possible to first form a solder layer on the surface to which the fiber or other component is to be bonded, bring the fiber (stripped of any polymeric cladding) or component into contact with the solder layer, and then add more of the solder to the interface (e.g., by use of a soldering iron) to promote bonding.

The solder typically exhibits desirable mechanical properties, including high creep resistance, e.g., a creep strain rate of less than 10% per year, advantageously less than 1% per year. This creep resistance is particularly attainable with Sn—Au or Sn—Ag compositions containing rare earths. Bonds made with the solder typically exhibit a shear strength of at least 15 psi. The tensile strength of the solder is reflected in the examples below.

A variety of articles are capable of being formed according to the invention. One type of device for which oxide-bondable solders are particularly useful is optical fiber grating devices, which include Bragg gratings, long period gratings and diffraction gratings.

Reconfigurability of grating wavelength is highly useful in all types of gratings, particularly for applications such as wavelength division multiplexing, in which there is a need to selectively choose a specific wavelength channel and perform operations such as add/drop, dispersion compensation and gain equalization. One way of achieving such reconfiguration of grating wavelength is by the application of a tensile or compressive strain on the fiber grating, the strain effectively altering the periodicity of the grating. In order to be strained, the optical fiber grating must be bonded, either at both ends or along the entire length, to an actuator mechanism (based on magnetic, thermal, piezoelectric or magnetostrictive means). The bond must be strong since a stress of 9000 psi is generally required to achieve a wavelength shift of 1 nm in a 0.125 μm diameter SiO₂ optical fiber (standard telecommunication fiber). The solders according to the invention are particularly useful for this purpose. Two examples of optical fiber grating devices that can be built using these solders are illustrated in FIGS. 5A and 5B.

FIG. 5A is a magnetically-tunable fiber grating device (see U.S. Pat. No. 5,781,677 to Jin et al.) in which the ends of a fiber grating 12 (formed in a fiber 11) are firmly attached to two programmable magnets 14, 15 by bonding layers 18, advantageously formed using the solder of the invention. The bonding layers 18 allow transmission of force between the magnets to the grating. The solder is shown as bonding layers 18. The programmable magnet materials advantageously have magnetic properties modifiable by a pulse magnetic field. One or more electromagnets (solenoids) 16, 17 are disposed adjacent the magnets 14, 15 for providing a controllable magnetic field between them. When a pulse magnetic field of appropriate sign and strength is applied by the electromagnets 16, 17, the similar magnetic poles that are adjacent (S adjacent S) are forced apart, producing a tensile strain on the fiber grating. If dissimilar magnetic poles were to be placed adjacent, they would be forced together, producing a compressive strain on the grating. The magnitude of the strain is able to be controlled by varying the strength of the applied pulsed magnetic field. Examples of suitable magnets include Fe—Cr—Co, Fe—Al—Ni—Co (Alnico), Cu—Ni—Fe (Cunife), Co—Fe—V (Vicalloy), specially-processed, low-coercivity (H_(c)) rare earth cobalt (Sm—Co) or Nd—Fe—B magnets, and Ba-ferrite or Sr-ferrite magnets. The presence of native oxides makes direct bonding (bonding without metallization) to some of these magnetic materials difficult, if not impossible, using conventional solders, thereby showing the significance of the solders of the invention to such applications.

FIG. 5B depicts a thermally-tunable grating device structure (see H. Mavoori et al., “Enhanced Thermal and Magnetic Actuation for Broad-Range Tuning of FBG-Based Reconfigurable Add/Drop Devices”, Optics Lett., Vol. 24, No. 11, 714 (1999)). In this device, the straining of the fiber grating 20 is performed by bonding the grating, along its whole length (with a bond layer 22), to a substrate material 24 with a high coefficient of thermal expansion (α). When the temperature of the substrate 24 is altered, the changes in dimension due to thermal contraction/expansion induce a strain on the grating 20, thereby altering the periodicity. It is possible to form the continuous bond 22 (which is in contrast to the discrete bonds in the device of FIG. 5A) using the solders of the invention, which avoid the need for intermediate metallization layers. The substrate material 24 is typically a metallic element such as Al (α=+23 ppm/° C.), a metallic alloy such as Ni—Ti (α=−20 to −200 ppm/° C.) or a ceramic such as ZrW₂O₈ (α=−5 to −11 ppm/° C.).

A variety of other electronic, opto-electronic and optical device structures are capable of being formed using the oxide-bonding solders of the invention. For example, in addition to bonding of optical fibers, bonding of a variety of other components such as planar waveguides (typically silica or phosphate glass), optical lenses, heat-spreaders such as BeO (used in laser packages) are possible.

The invention will be further clarified by the following examples, which are intended to be exemplary.

Comparative Example 1 (Prior Art Solder)

About 0.2 g of Sn-3.5 wt % Ag solder was melted inside a 0.5 inch diameter quartz (SiO₂) tube. One end of the quartz tube was attached to an argon gas source for continuous Ar flow to prevent oxidation of solder during melting and solder processing, while the other end was open for the argon gas to exit. Upon melting of the solder by sideways heating with a small gas torch, the Sn—Ag solder melted and balled up as a sphere with no sign of wetting of the quartz tube. Mechanically forced spreading of the molten solder by an optical fiber (SiO₂) inserted through the open end of the quartz tube did not cause any wetting on the quartz tube or optical fiber. The wetting angle of the molten solder on the quartz surface was greater than 100 degrees. Upon solidification of the solder, the solder slipped out of the quartz tube easily as a ball, with no sign of bonding to the quartz tube. Similar results were seen with Au-20 wt. % Sn solder.

EXAMPLE 2

0.235 g of Sn-3.5 wt % Ag solder and 0.005 g of lutetium (Lu) metal (about 2% by weight of the base solder) were melted together and alloyed inside a 0.5 inch diameter quartz (SiO₂) tube. One end of the quartz tube was attached to an argon gas source for continuous Ar flow to prevent oxidation of solder during melting and processing, while the other end was open. The melting and alloying of solder was carried out by heating with a small gas torch, as in Comparative Example 1.

After alloying and solidification of the solder inside the quartz tube, the torch flame was made weaker, and was used to reheat and melt the solder. The molten solder was then pushed around by a quartz rod from the open end of the quartz tube. Wherever the molten solder touched the quartz tube, the solder wet and spread onto the quartz. The solder also provided a relatively strong bond to the quartz tube surface upon subsequent cooling to room temperature. The wetting angle was less than 60 degrees and typically much less than 45 degrees.

The solder was then re-melted, and through the open end of the quartz tube was pushed a 0.005″ diameter., telecommunication-grade optical fiber (SiO₂) with the polymer coating stripped. The whole assembly was then allowed to cool to room temperature. In order to test the bond strength of the solder to the fiber and to the quartz, a weight of 0.5 lb., corresponding to a tensile stress of 26,000 psi, was placed on the free end of the optical fiber using a strong tape. The solder bond to the SiO₂ fiber as well as to the quartz tube remained strong without any mechanical failure.

Upon subsequent examination of the solder bonding to the quartz tube (inner surface), the solder could not be removed by mechanical force from the quartz tube surface. Continued force resulted in pulling of the solder from tube, but with fracturing and flaking of the quartz rather than breakage of the solder bond. Experiments with Sn—Ag solders containing Er gave similar results.

EXAMPLE 3

A SnAgLu solder of the same composition as Example 2 was formed, re-melted using a soldering tip, and then applied to a quartz substrate. FIG. 4A shows a cross-sectional microstructure (by transmission electron microscopy) of the quartz-solder interface bond area. The micrograph shows that the soldering process involved formation of an interfacial region on the order of 10-50 Angstroms thick. This interfacial region was composed of amorphous phases and crystalline phases, one of which was Lu₂O₃. Chemical analysis of this region, shown in FIG. 4B, indicated that the bonding element, Lu, segregated at the interface, thereby contributing to the bonding process.

The addition of the small amount of the rare earth Lu did not significantly affect the melting point of the Sn-3.5%Ag eutectic solder. DSC (differential scanning calorimetry) indicated that the melting point remained at a convenient low temperature of about 220° C.

EXAMPLE 4

A solder was made by melting together 3.17 g of Au, 0.807 g of Sn (about 20% by weight of the alloy) and 0.082 g of Lu (about 2% by weight) inside a {fraction (5/16)} inch diameter quartz (SiO₂) tube. One end of the tube was sealed while the other was attached to a mechanical vacuum pump to create a vacuum to prevent oxidation of the solder during the alloying process. Heating was accomplished using a small gas torch, as in the previous example. The solder was held molten at red-hot temperature (˜800° C.) for 3 minutes to allow sufficient time for inter-mixing of the constituents and homogenization of the composition. On solidification after alloying, it was observed that the solder had formed a strong bond wherever it touched the inner walls of the quartz tube. The bonding was so strong that the quartz tube had to be broken in order to free the pellet of the inventive solder, and even the freed pellet contained numerous small pieces of the shattered quartz.

EXAMPLE 5

To demonstrate the oxide-wetting ability of the solder of Example 4, the following experiment was conducted: The outside surface of a 0.180 inch stainless steel tube was flame-oxidized to make it non-wettable by conventional solders (as a result of the formation of a stable layer of chromium oxide). One end of an optical fiber was laid flat against this oxidized stainless steel surface and a small quantity (˜0.1 g) of the solder was used to bond the fiber to the stainless steel with the help of an ultrasonic hand-soldering iron. (The soldering operation was performed in air, without the use of any flux, and thus ultrasonics were used to break up the oxide layer formed at the surface of the molten solder. If the soldering were to be done in an oxygen-free atmosphere, e.g., in an inert-gas or reducing-gas atmosphere, such as nitrogen or argon or with a small addition of hydrogen or formic acid vapor, or if a suitable flux were to be used, a conventional soldering operation would tend to be sufficient). A weight of 0.8 lb., corresponding to a tensile stress of 42,000 psi was placed onto the other end of the bonded optical fiber. Under such tensile loading, the solder bond to the SiO₂ fiber as well as to the stainless steel surface remained secure with no sign of mechanical failure.

The addition of a small amount of rare earth Lu did not significantly alter the melting point of the Au-20% Sn solder, as established by differential scanning calorimetry (DSC), which indicated the melting point to remain at about 280° C.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. 

What is claimed is:
 1. An article comprising a solder composition that comprises 0.1 to 5 wt. % of one or more rare earth elements, and at least 0.1 wt. % Au, Ag, or mixtures thereof, based on the weight of the total composition, wherein the amount of Au, Ag, or mixtures thereof is sufficient to provide solubility for at least a portion of the rare earth elements, and wherein the solder composition comprises a base solder material consisting of Au, Ag, or mixtures thereof, or consisting of one or more solder materials other than Au and Ag, or consisting of Au, Ag, or mixtures thereof and one or more solder materials other than Au and Ag.
 2. The article of claim 1, wherein the amount of Au, Ag, or mixtures thereof is sufficient to provide solubility for substantially all the rare earth elements.
 3. The article of claim 1, wherein the solder composition comprises greater than 50 wt. % Au, Ag, or mixtures thereof.
 4. The article of claim 1, wherein the solder composition comprises 0.2 to 2 wt. % of the one or more rare earth elements.
 5. An article comprising a solder composition that comprises 0.01 to 20 wt. % of one or more rare earth elements, and 0.1 to 30 wt. % Au, Ag, or mixtures thereof, based on the weight of the total composition, wherein the amount of Au, Ag, or mixtures thereof is sufficient to provide solubility for at least a portion of the rare earth elements, and wherein the solder composition comprises a base solder material consisting of Au, Ag, or mixtures thereof, or consisting of one or more solder materials other than Au and Ag, or consisting of Au, Ag, or mixtures thereof and one or more solder materials other than Au and Ag.
 6. The article of claim 5, wherein the rare earth elements are present in an amount of 0.01 to 50 wt. % based on the weight of the Au, Ag, or mixtures thereof.
 7. The article of claim 6, wherein the solder composition comprises 0.2 to 5 wt. % Au, Ag or mixtures thereof.
 8. The article of claim 1, wherein the base solder material comprises one or more elements selected from the group consisting of Sn, Sb, In, Bi, Zn, and Pb.
 9. An article comprising a solder composition that consists essentially of a base solder material of Sn and at least 0.1 wt. % of Au or Ag, and 0.01 to 20 wt. % of one or more rare earth elements.
 10. The article of claim 9, wherein the rare earth elements are selected from the group consisting of Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
 11. The article of claim 9, wherein the solder composition exhibits a creep strain rate of less than 10% per year.
 12. An article comprising a solder composition that comprises 0.01 to 20 wt. % of one or more rare earth elements, and at least 0.1 wt. % Au, Ag, or mixtures thereof, based on the weight of the total composition, wherein the amount of Au, Ag, or mixtures thereof is sufficient to provide solubility for at least a portion of the rare earth elements, wherein the solder composition comprises a base solder material consisting of Au, Ag, or mixtures thereof, or consisting of one or more solder materials other than Au and Ag, or consisting of Au, Ag, or mixtures thereof and one or more solder materials other than Au and Ag, and wherein the solder is bonded to at least one oxide surface in the absence of any intermediate metallizing layers.
 13. A process for fabricating an article, comprising the step of bonding two or more components with a solder composition that comprises 0.1 to 5 wt. % of one or more rare earth elements, and at least 0.1 wt. % Au, Ag, or mixtures thereof, based on the weight of the total composition, wherein the amount of Au, Ag, or mixtures thereof is sufficient to provide solubility for at least a portion of the rare earth elements, and wherein the solder composition comprises a base solder material consisting of Au, Ag, or mixtures thereof, or consisting of one or more solder materials other than Au and Ag, or consisting of Au, Ag, or mixtures thereof and one or more solder materials other than Au and Ag.
 14. The process of claim 13, wherein the amount of Au, Ag, or mixtures thereof is sufficient to provide solubility for substantially all the rare earth elements.
 15. The process of claim 13, wherein the solder composition comprises greater than 50 wt. % of the Au, Ag, or mixtures thereof.
 16. The process of claim 13, wherein the solder composition comprises 0.2 to 2 wt. % of the one or more rare earth elements.
 17. A process for fabricating an article, comprising the step of bonding two or more components with a solder composition that comprises 0.01 to 20 wt. % of one or more rare earth elements, and 0.1 to 30 wt. % Au, Ag, or mixtures thereof, based on the weight of the total composition, wherein the amount of Au, Ag, or mixtures thereof is sufficient to provide solubility for at least a portion of the rare earth elements, and wherein the solder composition comprises a base solder material consisting of Au, Ag, or mixtures thereof, or consisting of one or more solder materials other than Au and Ag, or consisting of Au, Ag, or mixtures thereof and one or more solder materials other than Au and Ag.
 18. The process of claim 17, wherein the rare earth elements are present in an amount of 0.01 to 50 wt. % based on the weight of the Au, Ag, or mixtures thereof.
 19. The process of claim 18, wherein the solder composition comprises 0.2 to 5 wt. % Au, Ag or mixtures thereof.
 20. A process for fabricating an article, comprising the step of bonding two or more components with a solder composition that comprises 0.01 to 20 wt. % of one or more rare earth elements, and at least 0.1 wt. % Au, Ag, or mixtures thereof, based on the weight of the total composition, wherein the amount of Au, Ag, or mixtures thereof is sufficient to provide solubility for at least a portion of the rare earth elements, wherein the solder composition comprises a base solder material consisting of Au, Ag, or mixtures thereof, or consisting of one or more solder materials other than Au and Ag, or consisting of Au, Ag, or mixtures thereof and one or more solder materials other than Au and Ag, wherein at least one of the components comprises an oxide surface, and wherein the bonding is performed in the absence of an intermediate metallizing layer. 